Generally, many types of electrical devices may utilize analog signals that are continuously-variable, and effectively infinite in resolution in time and magnitude. For example, actuators and transducers, such as light emitting diodes (“LED”s), motors, robotic servos, heating elements, light dimmers, braking systems, and the like, receive analog input control signals to control their operation. That is, an input control signal may control the brightness of an LED or other type of lighting device, the speed of a motor, the heat output of a heating element, etc.
Generally, these types of devices alternatively may be controlled by digital controllers, such as microprocessors, digital signal processors, and microcontrollers, that generate a digitally-encoded version of an analog control signal. Devices such as switching amplifiers (e.g., for use in audio) and switched mode power supplies (e.g., for use in computers) also may utilize such digital control signals.
Generally a digital controller may modulate a digital signal through the use of pulse modulation to generate a digitally-encoded control signal representative of an analog signal. Pulse modulation modifies a parameter of a series of digital pulses in order to encode an analog signal level. By operating at a pulse frequency sufficiently above that which would or appear at have an adverse effect on the load, pulse modulation provides a digital signal appearing to the load as a steady voltage between the low and high values used for the load.
Several different types of modulation have been developed, including pulse amplitude modulation, pulse density modulation, and pulse width modulation. Pulse amplitude modulation generally modifies the amplitude of individual pulses to simulate voltages between a low level and a high level. Pulse density modulation generally modifies the density of the pulses in a pulse stream to represent different signal levels. Pulse width modulation generally modifies the duty cycle, or percentage of time that the signal is on, of a series of pulses by changing the pulse width, or duration of on-time, of individual pulses. Generally, pulse width modulation may be considered a special case of pulse density modulation in which all the pulses corresponding to one sample are contiguous in the digital signal.